1. Field of the Invention
This invention relates to a fuel injection nozzle body for fuel injection nozzles for internal combustion engines, particularly for high-speed diesel engines, which body comprises fuel injection holes, which extend from the seat surface for a nozzle needle. The invention relates also to a process of manufacturing such fuel injection nozzle body for internal combustion engines, and to apparatus for carrying out that process.
2. Description of the Prior Art
Fuel injection nozzles in which the fuel injection time is controlled by axially nozzle needles are known in the art. In those known designs the fuel injection holes extend either from a blind bore below the valve seat or from the region of the valve seat itself. In embodiments in which the fuel injection holes extend from the blind bores, an afterdripping has been observed. The afterdripping fuel is not adequately atomized and for this reason cannot be burnt so that the economy of the fuel consumption is reduced and the emission behavior, particularly the emission or unburnt hydrocarbons, is deteriorated.
In order to oppose such afterdripping it has already been proposed to arrange the fuel injection holes in the region of the seat for the nozzle needle. But the provision of fuel injection holes in the seat face itself gives rise to a number of manufacturing problems, which can be solved only with difficulty, and such fuel injection holes provided in the seat surface have always involved a high risk of fraction in experiments conducted in the past. For this reason nozzles formed with drilled holes in their seats are not made in series for high-speed diesel engines.
The stresses which arise in the material of the nozzle needle body adjacent to the seat for the nozzle needle and which may result in a fracture of the nozzle needle body consist of a number of individual stresses, which will be listed hereinafter by way of example. A pulsating hydrostatic pressure under an average supply pressure of about 200 bars will particularly give rise to high peripheral stresses and that pulsating hydrostatic pressure will obviously result also in high dynamic pressure peaks. In order to ensure a sealing of the fuel injection holes after the predetermined fuel injection time, the nozzle needle must impinge on the seat for the nozzle needle at relatively high velocity. The resulting longitudinal stresses in the nozzle needle body are superimposed on the high peripheral stresses which are due to the hydrostatic pressure. The fuel injection holes give rise to a pronounced notch effect so that any fracture will usually begin at the fuel injection holes. Besides, cavitation is often caused by the fuel at the entrance end of the fuel injection holes and gives rise to intergranular notches so that the inherent notch effect is inreased by the fuel injection holes. During operation, the outside surface of fuel injection nozzle bodies for internal combustion engines is exposed to temperature of an order of 350.degree. C. so that a relatively distinct temperature gradient is obtained over the wall thickness of the nozzle needle body and steeply decreases inwardly. There is also a corrosion by hot gases inside the nozzle body because combustion gases enter through the fuel injection holes. The cooperation of pulsating tensile stresses on three axes and of notch effects and corrosive actions is particularly undesirable.
A number of pressure and temperature treatments for tubes have been disclosed by which the strength properties of the walls of tubes can be improved. In particular, Published German Application No. 15 83 992 proposes to increase the strength of thick-walled tubes by a process comprising a plurality of consecutive operations in which, inter alia, a ball is driven through a tube having a nominal inside diameter which is smaller than the outside of the ball. It has also been disclosed to transform those zones within a tube which are loaded by pressure and stress by suitable combined temperature and pressure treatments through the tube thickness to a defined initial condition, which involves a tensile stress on the outside and a compressive stress on the inside.
In order to prevent a corrosion by hot gases inside the nozzle body the valve must close before the pressure in the combustion chamber, outside the nozzle body, exceeds the pressure inside the nozzle body. For this reason the closing of the valve must begin early and must be as fast as possible.
The closing begins as soon as the hydraulic force acting on the valve needle has decreased below the force of the closing spring. Because the hydraulic pressure acts on a larger surface area when the needle is open than when it is closed--the ratio of said surfaces is the closing ratio--the closing pressure will always be lower than the opening pressure. To ensure that the closing begins early, the seat diameter must be as small as possible although this will increase the pressure per unit of area of the valve seat.
A fast closing of the needle requires a hard closing spring, which will increase the impact of the needle on the valve seat.
From the aspect of strength as early and quick closing was not possible in the prior art.